1. Field of the Invention
The present invention relates, generally, to automotive lights and, more specifically, to an automotive light and a method of laser welding an automotive light.
2. Description of Related Art
The term “automotive light” as used in the related is known to refer to either a rear automotive light or a front automotive light (also known as a “headlight”) for use as lighting and/or signaling devices of a vehicle, which includes at least one external automotive light having a lighting and/or signaling function towards the outside of the vehicle (such as, for example: a sidelight, an indicator light, a brake light, a rear fog light, a reverse light, a dipped beam headlight, a main beam headlight, etc.).
The automotive light generally includes a container body, a lenticular body, and at least one light source. The lenticular body is placed so as to close a mouth of the container body so as to form a housing chamber. The light source is arranged inside the housing chamber, which may be directed so as to emit light towards the lenticular body when powered with electricity.
In manufacturing automotive lights, once the various components have been assembled, there needs to be attachment and hermetic sealing of the lenticular body to the container body. Typically, sealing is effected by welding. It will be appreciated that welding may also be utilized for other components of a more complex automotive light, for example components arranged inside the housing chamber.
The process of laser welding of polymeric bodies an automotive light makes it possible to combine a transmissive polymeric body capable of transmitting a laser radiation, and an absorbent polymeric body capable of absorbing the laser radiation. Here, the laser radiation is transformed into heat when it encounters the absorbent polymeric body which, by heating locally, transfers heat to the transmissive polymeric body, resulting in a softening and a local melting of both polymeric bodies which thus join firmly to each other.
By way of example, the absorbent polymeric body of the automotive light may include the container body, while the transmissive polymeric body may include the lenticular body, which closes the container body and forms a housing chamber for housing a light source of the automotive headlight. However, it will be appreciated that the absorbent and transmissive polymeric bodies can be realized generically by further polymeric components of the automotive headlight.
Laser welding processes of polymeric bodies of automotive lights can be difficult to implement because of the complex geometry of the polymeric bodies. For example, surface discontinuities of the transmissive polymeric body (such as fittings, ribs, grooves, prominences, curvatures, etc.) may obstruct the flow of the laser radiation towards the welding area, which is often distant from an emission point of the laser radiation. To overcome drawbacks of this kind, solutions known in the related art include providing a polymeric transmissive portion of the body acting as guide light of the laser radiation as described in U.S. Pat. No. 6,592,239B1; or an apparatus for simultaneous laser welding equipped with a distributor of laser radiation including a light guide formed of flat mirror-treated walls to focus the laser radiation. However, both of these expedients have poor performance, because only a small fraction of the laser radiation emitted by a laser emitter reaches the welding area (See FIGS. 1 and 2).
By way of example of the first solution described above, and with reference to FIGS. 1 and 2, a convex-shaped lenticular body may include a light guide end capable of channeling the laser radiation emitted by the laser towards the welding area, using at least one reflection of the laser radiation on the inner walls of the lenticular body. However, experimental tests have shown that the laser emitter and the light guide end of the lenticular body do not cooperate in a very effective manner since only a small portion of the laser radiation emitted by the laser emitter is channeled towards the welding area; specifically, only a fraction equal to 22% of the laser radiation emitted by the laser emitter reaches the welding area with a single reflection of the laser radiation, while this fraction decreases drastically with a plurality of reflections of the laser radiation, arriving at just 2% of the laser radiation emitted by the laser emitter.
In addition, the use of a portion of the transmissive lenticular body as a light guide proves to be a poor solution also in the case in which the lenticular body has a discontinuous surface. Moreover, the laser radiation may be deflected in an uncontrolled manner by the discontinuity, or the correct inclination of the laser radiation with respect to an input area of the lenticular body may be compromised in order to bypass the discontinuity, with consequent waste of laser radiation.
As an example of the second solution described above, and with reference to FIGS. 3 and 4, simulations of this welding process have shown that the distributor of the laser radiation including a light guide formed of flat mirror-treated walls is not able to directly route the laser radiation emerging from an outlet of the laser radiation distributor towards the welding area in some situations, particularly if the lenticular body is a curved shape. The laser radiation distributor may, in fact, sometimes not find any location close to a face of the lenticular body, because the laser radiation distributor would physically interfere with the lenticular body.
In addition, the use of the laser radiation distributor including mirror-treated flat walls proves an arguable solution even in the case in which the lenticular body presents a surface discontinuity. In fact, a substantial proportion of the laser radiation emerging from the outlet of the laser radiation distributor is deflected in an uncontrolled manner by the surface discontinuity of the lenticular body without reaching the welding area.
Thus, conventional laser welding applications and techniques used with automotive lights are not very efficient because of the complex geometries of automotive lights to be welded. In fact, the lenticular bodies and the container bodies of automotive lights are made of polymeric materials and include highly complex geometries with curved or straight coupling surfaces with highly variable inclinations along the entire perimeter of the mutual coupling. The complex geometry of automotive lights or their components (such as the container body and the lenticular body) are ill-adapted to current laser welding techniques which are in fact optimized for applications on flat walls, simple geometries, and relatively thin thicknesses of the bodies. Thus, laser welding techniques are currently little used on automotive lights in that there is no guarantee of satisfactory results and alternative welding techniques are more cost/time competitive (such as vibration, ultrasound, and friction welding, etc.).
In addition, certain complexities of automotive lights further discourages and makes current laser welding techniques inconvenient. By way of example, a component of the automotive light (such as the lenticular body) can be crossed by light emitted by the light source so as to effect lighting of the automotive light. The lenticular body may have a coloration so as ensure that the color of the light emitted by the light source complies with government-mandated regulations (for example, a stop light of the automotive light may be realised with a substantially white light source and a lenticular body tending to red). However, during the laser welding process, a red colored lenticular body absorbs a lot of light energy in comparison to a clear lenticular body to the detriment of the light energy provided by the laser source, which needs to be able to provide a predetermined light energy in the welding area. The increased absorption due to the presence of a colored lenticular body acting as the transmission element, which filters the radiation emitted, requires the use of higher power laser beams, which consequently results in high energy consumption and increased welding costs. This way, the energy efficiency of the laser welding of lenticular bodies is further reduced: absorbing (inasmuch as colored) a significant portion of light radiation; and dispersing well over half due to the complex geometries of the lenticular bodies themselves.
Because of the foregoing considerations, laser welding techniques are little used on conventional automotive lights since they are too complex, expensive, and inconvenient to implement when compared to alternative welding techniques, such as ultrasonic welding. Thus, there remains a need in the art for a laser welding method of polymeric bodies used in automotive lights able to reduce the power of the laser source.